Parasitic Bird Fights Evolutionary Arms Race… With Itself

Parasitic Bird Fights Evolutionary Arms Race… With Itself

In the image above, all the eggs in the top row are laid by cuckoos and those in the bottom row belong to their victims. These uncanny similarities help cuckoos to fob off their parental duties by laying their eggs in the nests of other species. If the hosts can’t tell the difference between their eggs and the foreign ones, they’ll end up raising the cuckoo chick as their own. And they pay a hefty price for their gullibility, since cuckoo chicks often kill or outcompete their foster siblings.

The relationship between cuckoos and their hosts is a classic example ofan evolutionary arms race. Cuckoos, should evolve eggs that more closely match those of their hosts, while the hosts should evolve keener senses to discriminate between their own eggs and a cuckoo’s.

But in Africa, this classic story takes an unusual twist.

The greater honeyguide isn’t a cuckoo but uses the same tactics—it parasitises the nests of little bee-eaters by laying eggs of the same size and shape. But this mimicry doesn’t help it to fool the bee-eaters, which seem to accept any old egg no matter how different it looks. Instead, Claire Spottiswoode from the University of Cambridge has found that the parasitic honeyguides are fighting an evolutionary arms race against… each other.

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The behavior of cuckoo hatched chicks has always disturbed me. Here is a few minute old, completely blind chick that knows enough to push the other unhatched eggs of its host bird out of the nest. It was even freakier to see two simultaneously hatched cuckoo chicks trying to push each other out of the host nest. This complicated behavior of pushing a heavy object up and over a nest rim just boggles my mind. How can a tiny just-hatched bird that can’t see even come up with such an idea? That this complicated behavior is purely instinctual really makes me wonder about how much of human behavior is really instinctual.

The behavior of cuckoo hatched chicks has always disturbed me. Here is a few minute old, completely blind chick that knows enough to push the other unhatched eggs of its host bird out of the nest. It was even freakier to see two simultaneously hatched cuckoo chicks trying to push each other out of t…

If you haven’t already read it I highly recommend Steven Pinker’s book The Blank Slate. Its filled with examples like that and it really shows that a lot of behavior and probably even our whole way of conceptualizing the world, are in many ways hard coded into our genes.

The behavior of cuckoo hatched chicks has always disturbed me. Here is a few minute old, completely blind chick that knows enough to push the other unhatched eggs of its host bird out of the nest. It was even freakier to see two simultaneously hatched cuckoo chicks trying to push each other out of t…

Natural selection, of course.

The first chick that even intimated such behavior had a slight reproductive advantage. Say no more than crowding the resident chick to the side, or being born earlier. Then it’s descendents would have this propensity and further descendents could build on this to the fully parasitical behavior we see today.

I watched on a David Attenborough program of course, a cuckoo hatchling push 2 of its foster siblings out of the nest in full view of its foster parent, who went on to raise the cuckoo chick regardless. We are definitely born selfish.

If cuckoo females have eggs matched to a particular species presumably the young will inherit that trait so only parasitise that species? Is this trait passed only down the female line or do the males also mate only with females that parasitise a certain species? (How would they know?) If so is there a case for regarding cuckoos as different species or sub-species depending on which host species they are parasites of?

If cuckoo females have eggs matched to a particular species presumably the young will inherit that trait so only parasitise that species? Is this trait passed only down the female line or do the males also mate only with females that parasitise a certain species? (How would they know?) If so is ther…

Good question. Another alternative explanation is that it may be environment dependent. I.e., Cuckoos in one area mimic X birds and Cuckoos in a different area mimic Y birds.

If cuckoo females have eggs matched to a particular species presumably the young will inherit that trait so only parasitise that species? Is this trait passed only down the female line or do the males also mate only with females that parasitise a certain species? (How would they know?) If so is ther…

Birds are opposite to us (mammals) when it comes to XY chromosomes. Females are XY and males are XX in birds. If the gene that mimics the host colour is in the Y chromosose it get passed on un-contaminated by the male. So any old male cuckoo can mate with a female cuckoo without contaminating/stomping her “mimicry” gene.

If cuckoo females have eggs matched to a particular species presumably the young will inherit that trait so only parasitise that species? Is this trait passed only down the female line or do the males also mate only with females that parasitise a certain species? (How would they know?) If so is ther…

Throughout an individual common cuckoo’s life, every egg she lays will mimic the same host species. And her daughters will lay eggs which look just like mums eggs.

These different types of females are called gentes. They are not a separate species or subspecies as they can mate with any male, irrespective of the colour or pattern of the egg from which he hatched. Research strongly suggests that they mate randomly.

A possible answer as to how she knows which nest to lay them in could be imprinting: she remembers her foster mother’s song.

Your guess that this comes down the female line (the W chromosome) looks more than likely but, to my knowledge, nobody has done the work yet.

A possible answer as to how she knows which nest to lay them in could be imprinting: she remembers her foster mother’s song

Great comment, thanks for the info. Isn’t it also possible that the “knowing” is just genetic as well, besides inheriting a gene that makes the eggs look like a different species she also inherits the knowledge of where to lay them?

Spottiswoode filmed this brutal behaviour in 2011, and she showed that honeyguides are a huge problem. **Two-thirds
** of the nests are parasitised, and a third of these contain eggs from more than one honeyguide.

When does the run-away-train effect happen? Two-thirds is amazing. How can the bee-eaters population do anything but decline? If the honeyguide endangers or eliminates the bee-eater will it (can it) find another host? Can it raise its own? Has it raised its own in the past? Will it remember how?